1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition and, more particularly, to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation, for example, ultraviolet rays such as g-line or i-line, (extreme) deep ultraviolet rays such as a KrF excimer laser, ArF excimer laser, F2 excimer laser, or EUV, X-rays such as synchrotron radiation, and charged particle rays such as electron beams. The present invention also relates to a novel copolymer useful as a copolymer component for the resin composition and to a polymer mixture containing the copolymer.
2. Description of Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, photolithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in recent years in order to achieve a higher degree of integration.
A conventional photolithographic process utilizes near ultraviolet rays such as i-line radiation. It is known in the art that microfabrication with a line width of a sub-quarter micron order using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 μm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), an F2 excimer laser (wavelength: 157 nm), and EUV (wavelength: 13 nm, etc., extreme ultraviolet radiation) have attracted attention.
As a radiation-sensitive resin composition applicable to shorter wavelength radiation, a number of compositions utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation-sensitive composition.
As the chemically-amplified radiation-sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a resin containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the resin to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
Micronization of photolithography processes in recent years has been remarkable. In particular, in the KrF photolithography processes the limit resolution has decreased to one half of the light source wavelength or less. For this reason, characteristics required for photo resists have become increasingly stringent. In particular, there is urgent need for the improvement in the resolution performance, radiation transmittance, and dry etching resistance. As factors affecting the resolution of chemically-amplified resists, an activation energy required for dissociation of protection groups in an acid-dissociable resin,; difference in the dissolution rate in the developer before and after the dissociation, and the like can be given. From the viewpoint of the dissolution rate, an acrylic acid/phenol hybrid type (or an ESCAP-type) represented by protection of carboxylic acid with a t-butyl group is more advantageous than a pure phenol resin represented by protection of phenol with a t-butyl carbonate group. From the viewpoint of the activation energy, resins containing many alkyl-substituents having a large steric hindrance and acting as an electron donor are more preferable. For these reasons, Japanese Patent Application Laid-open No. 347405/2000 discloses a photo resist using an acrylic acid ester having a cycloalkyl group as a protection group. The composition disclosed by this patent application contains styrene units introduced to compensate poor dry etching resistance of the acrylic acid ester, with a consequence of sacrificing the advantage of superior resolution.
An object of the present invention is to provide a radiation-sensitive resin composition useful as a chemically amplified resist sensible to active radiations, for example, deep ultraviolet rays represented by a KrF excimer laser, ArF excimer laser, F2 excimer laser, and EUV excimer laser, exhibiting high resolution and high radiation transmittance, without impairing dry etching resistance.
Another object of the present invention is to provide a copolymer and a polymer mixture useful as a polymer component for the radiation-sensitive resin composition.